Exemplary embodiments of the present invention relate to a memory device using a semiconductor and a manufacturing method thereof, and more particularly, to a memory device using a magnetoresistive memory and a manufacturing method thereof.
A dynamic random access memory (DRAM) is a widely used semiconductor memory. However, a DRAM is reaching limits in scaling-down and obtaining adequate capacitance for capacitors in storing data. To address such features, different types of memory devices are being developed including a magnetoresistive random access memory (MRAM) using tunneling magneto-resistance.
An MRAM is a nonvolatile memory device to store data using a magneto-resistance change depending on magnetization directions of two ferromagnetic layers constituting a magnetic tunnel junction (MTJ). The MTJ has a stack structure of a ferromagnetic layer, an insulation layer, and a ferromagnetic layer. At this time, one of the two ferromagnetic layers is a pinned layer (PL) whose magnetization direction is pinned, and the other is a free layer (FL) whose magnetization direction is changed by a current passing therethrough.
When electrons tunneling through the first ferromagnetic layer pass through the insulation layer used as a tunneling barrier, the tunneling probability changes depending on the magnetization direction of the second ferromagnetic layer. More specifically, the tunneling probability is the highest when the magnetization directions of the two ferromagnetic layers are parallel to each other and is the lowest when the magnetization directions of the two ferromagnetic layers are anti-parallel to each other. Therefore, stored data can be read by using a difference in current generated in each case.
An MRAM uses a spin transfer torque (STT) phenomenon to write data to a memory cell. The STT phenomenon refers to a phenomenon that a spin-polarized current is transferred as an angular momentum of a ferromagnetic material by a change of an angular momentum instantly generated when the spin-polarized current passes through the ferromagnetic material. More specifically, when a high-density current having a polarized spin direction is applied to a ferromagnetic material, data is written using a phenomenon where a spin direction of a current is aligned when a magnetization direction of a ferromagnetic material does not correspond to a spin direction of a current.
In an MTJ used in a semiconductor memory, when electrons flow from a pinned layer to a free layer, the magnetization direction of the free layer corresponds to the magnetization direction of the pinned layer due to a flow of electrons whose spin directions are aligned in the magnetization direction of the pinned layer. On the other hand, when electrons flow from the free layer to the pinned layer, a spin accumulation phenomenon occurs at an interface between the pinned layer and the free layer, so that the magnetization direction of the free layer is anti-parallel to the magnetization direction of the pinned layer. Therefore, data can be written in the magnetization direction of the free layer.